added a function for getting space for ancestor nodes in the node_chain, and use it within dns_rbt_findnode.
added a function for getting space for ancestor nodes in the node_chain,
and use it within dns_rbt_findnode.

moved the guts of dns_rbt_deletename into its own function to clean up
the freeing of ancestor memory into just one location.

deletefromlevel required that ancestor_count be > 1, which would abort
trying to delete the root of the tree when the root had no children.

each/bind9-collab,pecharmin/bind9,each/bind9-collab,pecharmin/bind9,each/bind9-collab,pecharmin/bind9,pecharmin/bind9,each/bind9-collab,each/bind9-collab,each/bind9-collab,pecharmin/bind9,pecharmin/bind9